2 Functional Properties of Neurons 1 Irritability Ability
2 Functional Properties of Neurons 1. Irritability § Ability to respond to stimuli 2. Conductivity § Ability to transmit an impulse Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
How neurons communicate Action Potential (Nerve Impulse) § electrical signal that travels on the membrane of a neuron § based on movements of ions between the outside and inside of the cell Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Steps to a Nerve Impulse § Polarized: Resting neuron § Inside membrane is slightly – § Outside membrane is slightly + § Most membrane channels are closed, some diffusion of K+ or Na+ between cell and the environment through the sodium/potassium pump (active transport) § Stimulus Occurs § Light, sound, pressure, drugs, neurotransmitter… § If the stimulus reaches threshold then an action potential is started in the neuron and will travel down the membrane (This is called a nerve impulse) This is the ALL or NONE PRINCIPLE. Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Steps to a Nerve Impulse Depolarization § Sodium (Na+) channels open allowing Na+ to diffuse into the cell quickly § This causes the inside to become + (outside -) Repolarize: K+ gates open in order to allow K+ to diffuse out of the cell – this restores the membrane (+ outside, - inside) Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Figure 7. 9 a–b Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Nerve Impulses § Refractory Period § K+ must be moved back to the inside of the cell and NA+ must be pumped out of the cell in order to prepare for the next impulse § The sodium-potassium pump ( a membrane channel), using ATP, restores the original configuration Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Nerve Impulses Figure 7. 9 e–f Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Simple Video showing Action Potential § http: //video. google. com/videoplay? docid=6890770586678681705&ei=3 qb 9 Sq. Px. O 5_ar. QKQpin. BA&hl=en# § http: //outreach. mcb. harvard. edu/animations/actio npotential. swf § http: //video. google. com/videoplay? docid=6890770586678681705&ei=3 qb 9 Sq. Px. O 5_ar. QKQpin. BA&hl=en#docid=-4821246047499143591 Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Transmission of a Signal at Synapses § Impulses are able to cross the synapse to another nerve § Neurotransmitter is released from a nerve’s axon terminal http: //highered. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=swf: : 535: : /sites/dl/free/0072437316/120068/bio 02. s wf: : Endocytosis%20 and%20 Exocytosis § The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter § An action potential is started in the dendrite Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Transmission of a Signal at Synapses Axon of transmitting neuron Axon terminal Action potential arrives Vesicles Synaptic cleft Receiving neuron Synapse Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Synaptic cleft Ion channels Neurotransmitter binds to receptor on receiving neuron’s membrane Receiving neuron Neurotransmitter Receptor Neurotransmitter broken down and released Na+ Ion channel opens Ion channel closes Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 7. 10
Transmission of a Signal at Synapses Axon of transmitting neuron Axon terminal Action potential arrives Vesicles Synaptic cleft Receiving neuron Synapse Figure 7. 10, step 1 Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Transmission of a Signal at Synapses Axon of transmitting terminal neuron Vesicles Action potential arrives Synaptic cleft Receiving neuron Synapse Transmitting neuron Vesicle fuses with plasma membrane Synaptic cleft Ion channels Receiving neuron Figure 7. 10, step 2 Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Transmission of a Signal at Synapses Axon of terminal transmitting neuron Vesicles Action potential arrives Synaptic cleft Receiving neuron Synapse Transmitting neuron Vesicle fuses with plasma membrane Synaptic cleft Ion channels Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Receiving neuron Figure 7. 10, step 3 Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Transmission of a Signal at Synapses Axon of terminal transmitting neuron Vesicles Action potential arrives Synaptic cleft Receiving neuron Transmitting neuron Vesicle fuses with plasma membrane Synaptic cleft Ion channels Neurotransmitter is released into synaptic cleft Synapse Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter molecules Receiving neuron Figure 7. 10, step 4 Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings
Transmission of a Signal at Synapses Axon of terminal transmitting neuron Vesicles Action potential arrives Synaptic cleft Receiving neuron Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter molecules Synaptic cleft Ion channels Synapse Receiving neuron Neurotransmitter Receptor Na+ Ion channel opens Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 7. 10, step 5
Transmission of a Signal at Synapses Axon of terminal transmitting neuron Vesicles Action potential arrives Synaptic cleft Receiving neuron Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter molecules Synaptic cleft Ion channels Synapse Receiving neuron Neurotransmitter Receptor Na+ Ion channel opens Neurotransmitter broken down and released Na+ Ion channel closes Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 7. 10, step 6
Transmission of a Signal at Synapses Axon terminal Axon of transmitting neuron Action potential arrives Vesicles Synaptic cleft Receiving neuron Synapse Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Synaptic cleft Ion channels Neurotransmitter binds to receptor on receiving neuron’s membrane Receiving neuron Neurotransmitter Receptor Na+ Ion channel opens Neurotransmitter broken down and released Na+ Ion channel closes Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 7. 10, step 7
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